The invention relates to an aircraft undercarriage including a safety device having a predetermined breaking load such that the undercarriage is caused to become detached from the aircraft without damaging the wings or any other essential structural parts thereof, in the event of excessive longitudinal stresses being applied to the bottom part of the landing gear, for example at the level of the wheels.
It is known that an undercarriage can be mounted on the frame of the aircraft by way of an articulated connection which allows the undercarriage to be lowered and retracted. In the case of wing-mounted landing gear there is usually a front connection and a rear connection for the mounting of each undercarriage, such connections generally being provided on the rear spare of the respective wing.
In the event of a landing at excessive speed, or if the aircraft, leaving a runway for some reason, strikes a slope or any other obstacle to the free rolling movement of the undercarriage over the ground, the undercarriage and the part of the frame of the aircraft on which it is mounted are called upon to suffer quite considerable longitudinal stresses which can result in deformation and even fracture of the respective wing spar. This, already serious in itself and probably necessitating considerable repairs to the frame of the aircraft, it likely also to result in rupture of wing fuel tanks, which may result in the aircraft catching fire.
Various international safety regulations stipulate that undercarriages for commercial aircraft must be equipped with safety devices of predetermined breaking load which act as mechanical fuses, so that the undercarriage is capable of giving way under the effect of excessive longitudinal stresses without damaging the frame of the aircraft.
Such safety devices as are already known are generally located and extend at right-angles to the front mounting of the landing gear on the frame of the aircraft and fracture under specific traction and/or shearing stresses, which of course are vastly greater than the stresses likely to arise during normal landing, thereby to remove a direct connection of the undercarriage to the frame, and leaving the undercarriage free to fold back towards the rear of the aircraft.
A major disadvantage of previously proposed devices is that they do not prevent damage or even fracture of a part of the aircraft frame, particularly part of the wings, with the already stated risks which this entails.